Six steps to hell – Mark Lynas
By the end of the century, the Earth could be more than 6C hotter than
it is today, according to the Intergovernmental Panel on Climate
Change. We know that would be bad news – but just how bad? How big a
rise will it take for the Alps to melt, the oceans to die and desert
to conquer Europe and the Americas? Mark Lynas sifted through
thousands of scientific papers for his new book on global warming.
This is what the research told him …
Monday April 23, 2007 The Guardian
Nebraska isn’t at the top of most tourists’ to-do lists. However, this
dreary expanse of impossibly flat plains sits in the middle of one of
the most productive agricultural systems on Earth. Beef and corn
dominate the economy, and the Sand Hills region – where low, grassy
hillocks rise up from the flatlands – has some of the best cattle
ranching in the whole US. But scratch beneath the grass and you will
find, as the name suggests, not soil but sand. These innocuous-looking
hills were once desert, part of an immense system of sand dunes that
spread across the Great Plains from Texas in the south to the Canadian
prairies in the north. Six thousand years ago, when temperatures were
about 1C warmer than today in the US, these deserts may have looked
much as the Sahara does today. As global warming bites, the western US
could once again be plagued by perennial drought – devastating
agriculture and driving out human inhabitants on a scale far larger
than the 1930s “Dustbowl” exodus.
On the other side of the Atlantic, today’s hottest desert could be
seeing a wetter future in the one-degree world. At the same time as
sand dunes were blowing across the western US, the central Sahara was
a veritable Garden of Eden as rock paintings of elephants, giraffes
and buffalo, also dating from 6,000 years ago, attest. On the borders
of what is today Chad, Nigeria and Cameroon, the prehistoric Lake
Mega-Chad spread over an area only slightly smaller than the Caspian
Sea does now. Could a resurgent north African monsoon drive rainfall
back into the Sahara in a one-degree world? Models suggest it could.
Also in Africa, Mount Kilimanjaro will be losing the last of its snow
and ice as temperatures rise, leaving the entire continent ice-free
for the first time in at least 11,000 years. The Alps, too, will be
melting, releasing deadly giant landslides as thawing permafrost
removes the “glue” that holds the peaks together. In the Arctic,
temperatures will rise far higher than the one-degree global average,
continuing the rapid decline in sea ice that scientists have already
observed. This spells bad news for polar bears, walruses and ringed
seals – species that are effectively pushed off the top of the planet
as warming shrinks cold areas closer and closer to the pole.
Indeed, it is the ecological effects of warming that may be most
apparent at one degree. Critically, this temperature rise may wipe out
the majority of the world’s tropical coral reefs, devastating marine
biodiversity. Most of the Great Barrier Reef will be dead.
In the highly unlikely event that global warming deniers prove to be
right, we will still have to worry about carbon dioxide, because it
dissolves in the oceans and makes them more acidic. Even with
relatively low emissions, large areas of the southern oceans and parts
of the Pacific will within a few decades become toxic to organisms
with calcium carbonate shells, for the simple reason that the acidic
seawater will dissolve them. Many species of plankton – the basis of
the marine food chain and essential for the sustenance of higher
creatures, from mackerel to baleen whales – will be wiped out, and the
more acidic seawater may be the knockout blow for what remains of the
world’s coral reefs. The oceans may become the new deserts as the
world’s temperatures reach 2C above today’s.
Two degrees may not sound like much, but it is enough to make every
European summer as hot as 2003, when 30,000 people died from
heatstroke. That means extreme summers will be much hotter still. As
Middle East-style temperatures sweep across Europe, the death toll may
reach into the hundreds of thousands. The Mediterranean area can
expect six more weeks of heatwave conditions, with wildfire risk also
growing. Water worries will be aggravated as the southern Med loses a
fifth of its rainfall, and the tourism industry could collapse as
people move north outside the zones of extreme heat.
Two degrees is also enough to cause the eventual complete melting of
the Greenland ice sheet, which would raise global sea levels by seven
metres. Much of the ice-cap disappeared 125,000 years ago, when global
temperatures were 1-2C higher than now. Because of the sheer size of
the ice sheet, no one expects this full seven metres to come before
the end of the century, but a top Nasa climate scientist, James
Hansen, is warning that the mainstream projections of sea level rise
(of 50cm or so by 2100) could be dangerously conservative. As if to
underline Hansen’s warning, the rate of ice loss from Greenland has
tripled since 2004.
This melting will also continue to affect the world’s mountain ranges,
and in Peru all the glaciers will disappear from the Andean peaks that
currently supply Lima with water. In California, the loss of snowpack
from the Sierra Nevada – three-quarters of which could disappear in
the two-degree world – will leave cities such as Los Angeles
increasingly thirsty during the summer. Global food supplies,
especially in the tropics, will also be affected but while two degrees
of warming will be survivable for most humans, a third of all species
alive today may be driven to extinction as climate change wipes out
their habitat.
Scientists estimate that we have at best 10 years to bring down global
carbon emissions if we are to stabilise world temperatures within two
degrees of their present levels. The impacts of two degrees warming
are bad enough, but far worse is in store if emissions continue to
rise. Most importantly, 3C may be the “tipping point” where global
warming could run out of control, leaving us powerless to intervene as
planetary temperatures soar. The centre of this predicted disaster is
the Amazon, where the tropical rainforest, which today extends over
millions of square kilometres, would burn down in a firestorm of epic
proportions. Computer model projections show worsening droughts making
Amazonian trees, which have no evolved resistance to fire, much more
susceptible to burning. Once this drying trend passes a critical
threshold, any spark could light the firestorm which destroys almost
the entire rainforest ecosystem. Once the trees have gone, desert will
appear and the carbon released by the forests’ burning will be joined
by still more from the world’s soils. This could boost global
temperatures by a further 1.5=BAC – tippping us straight into the
four-degree world.
Three degrees alone would see increasing areas of the planet being
rendered essentially uninhabitable by drought and heat. In southern
Africa, a huge expanse centred on Botswana could see a remobilisation
of old sand dunes, much as is projected to happen earlier in the US
west. This would wipe out agriculture and drive tens of millions of
climate refugees out of the area. The same situation could also occur
in Australia, where most of the continent will now fall outside the
belts of regular rainfall.
With extreme weather continuing to bite – hurricanes may increase in
power by half a category above today’s top-level Category Five – world
food supplies will be critically endangered. This could mean hundreds
of millions – or even billions – of refugees moving out from areas of
famine and drought in the sub-tropics towards the mid-latitudes. In
Pakistan, for example, food supplies will crash as the waters of the
Indus decline to a trickle because of the melting of the Karakoram
glaciers that form the river’s source. Conflicts may erupt with
neighbouring India over water use from dams on Indus tributaries that
cross the border.
In northern Europe and the UK, summer drought will alternate with
extreme winter flooding as torrential rainstorms sweep in from the
Atlantic – perhaps bringing storm surge flooding to vulnerable
low-lying coastlines as sea levels continue to rise. Those areas still
able to grow crops and feed themselves, however, may become some of
the most valuable real estate on the planet, besieged by millions of
climate refugees from the south.
At four degrees another tipping point is almost certain to be crossed;
indeed, it could happen much earlier. (This reinforces the
determination of many environmental groups, and indeed the entire EU,
to bring us in within the two degrees target.) This moment comes as
the hundreds of billions of tonnes of carbon locked up in Arctic
permafrost – particularly in Siberia – enter the melt zone, releasing
globally warming methane and carbon dioxide in immense quantities. No
one knows how rapidly this might happen, or what its effect might be
on global temperatures, but this scientific uncertainty is surely
cause for concern and not complacency. The whole Arctic Ocean ice cap
will also disappear, leaving the North Pole as open water for the
first time in at least three million years. Extinction for polar bears
and other ice-dependent species will now be a certainty.
The south polar ice cap may also be badly affected – the West
Antarctic ice sheet could lift loose from its bedrock and collapse as
warming ocean waters nibble away at its base, much of which is
anchored below current sea levels. This would eventually add another
5m to global sea levels – again, the timescale is uncertain, but as
sea level rise accelerates coastlines will be in a constant state of
flux. Whole areas, and indeed whole island nations, will be submerged.
In Europe, new deserts will be spreading in Italy, Spain, Greece and
Turkey: the Sahara will have effectively leapt the Straits of
Gibraltar. In Switzerland, summer temperatures may hit 48C, more
reminiscent of Baghdad than Basel. The Alps will be so denuded of snow
and ice that they resemble the rocky moonscapes of today’s High Atlas
– glaciers will only persist on the highest peaks such as Mont Blanc.
The sort of climate experienced today in Marrakech will be experienced
in southern England, with summer temperatures in the home counties
reaching a searing 45C. Europe’s population may be forced into a
“great trek” north.
To find out what the planet would look like with five degrees of
warming, one must largely abandon the models and venture far back into
geological time, to the beginning of a period known as the Eocene.
Fossils of sub-tropical species such as crocodiles and turtles have
all been found in the Canadian high Arctic dating from the early
Eocene, 55 million years ago, when the Earth experienced a sudden and
dramatic global warming. These fossils even show that breadfruit trees
were growing on the coast of Greenland, while the Arctic Ocean saw
water temperatures of 20C within 200km of the North Pole itself. There
was no ice at either pole; forests were probably growing in central
Antarctica.
The Eocene greenhouse event fascinates scientists not just because of
its effects, which also saw a major mass extinction in the seas, but
also because of its likely cause: methane hydrates. This unlikely
substance, a sort of ice-like combination of methane and water that is
only stable at low temperatures and high pressure, may have burst into
the atmosphere from the seabed in an immense “ocean burp”, sparking a
surge in global temperatures (methane is even more powerful as a
greenhouse gas than carbon dioxide). Today vast amounts of these same
methane hydrates still sit on subsea continental shelves. As the
oceans warm, they could be released once more in a terrifying echo of
that methane belch of 55 million years ago. In the process, moreover,
the seafloor could slump as the gas is released, sparking massive
tsunamis that would further devastate the coasts.
Again, no one knows how likely this apocalyptic scenario is to unfold
in today’s world. The good news is that it could take centuries for
warmer water to penetrate down to the bottom of the oceans and release
the stored methane. The bad news is that it could happen much sooner
in shallower seas that see a stronger heating effect (and contain lots
of methane hydrate) such as in the Arctic. It is also important to
realise that the early Eocene greenhouse took at least 10,000 years to
come about. Today we could accomplish the same feat in less than a
century.
If there is one episode in the Earth’s history that we should try
above all not to repeat, it is surely the catastrophe that befell the
planet at the end of the Permian period, 251 million years ago. By the
end of this calamity, up to 95% of species were extinct. The
end-Permian wipeout is the nearest this planet has ever come to
becoming just another lifeless rock drifting through space. The
precise cause remains unclear, but what is undeniable is that the
end-Permian mass extinction was associated with a super-greenhouse
event. Oxygen isotopes in rocks dating from the time suggest that
temperatures rose by six degrees, perhaps because of an even bigger
methane belch than happened 200 million years later in the Eocene.
Sedimentary layers show that most of the world’s plant cover was
removed in a catastrophic bout of soil erosion. Rocks also show a
“fungal spike” as plants and animals rotted in situ. Still more
corpses were washed into the oceans, helping to turn them stagnant and
anoxic. Deserts invaded central Europe, and may even have reached
close to the Arctic Circle.
One scientific paper investigating “kill mechanisms” during the
end-Permian suggests that methane hydrate explosions “could destroy
terrestrial life almost entirely”. Acting much like today’s fuel-air
explosives (or “vacuum bombs”), major oceanic methane eruptions could
release energy equivalent to 10,000 times the world’s stockpile of
nuclear weapons.
Whatever happened back then to wipe out 95% of life on Earth must have
been pretty serious. And while it would be wrong to imagine that
history will ever straightforwardly repeat itself, we should certainly
try and learn the lessons of the distant past. If they tell us one
thing above all, it is this: that we mess with the climatic thermostat
of this planet at our extreme – and growing – peril.